System and method for distinguishing electrical events originating in the atria from far-field electrical events originating in the ventricles as detected by an implantable medical device

ABSTRACT

The system and method discriminates P-waves or other electrical events originating in the atria from R-waves or other electrical events originating in the ventricles. In one example, far-field R-waves in the atria are distinguished from true P-waves using both a post-ventricular atrial blanking (PVAB) interval and a separate pre-ventricular blanking interval (pre-VAB) interval. Insofar as the pre-VAB interval is concerned, upon detection of a P-wave in the atria, the implantable medical device begins tracking a pre-VAB interval. If an R-wave is then detected in the ventricles during the pre-VAB interval, the P-wave is rejected as being a far-field R-wave. A PVAB interval may also be employed to filter out any P-waves detected in the atria immediately following detection of an R-wave in the ventricles. In another example, far-field R-waves are distinguished from true P-waves using template matching. P-waves detected in the atria are compared against a template representative of true P-waves. If the P-wave substantially matches the template, the P-wave is deemed to be a true P-wave; otherwise, the P-wave is rejected as being a far-field R-wave or other anomalous electrical event. In both examples, the techniques are applicable to other types of electrical events detected within the heart besides P-waves and R-waves, such as electrical events occurring during fibrillation or flutter when discrete P-waves and R-waves may not be detectable.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/173,417, filed Dec. 28, 1999; and is related to copending U.S.Provisional No. 60/173,341, filed Dec. 28, 1999.

FIELD OF THE INVENTION

The invention generally relates to implantable medical devices, such aspacemakers or implantable cardioverter-defibrillators (“ICDs”) and, inparticular, to techniques for analyzing electrical events detectedwithin the heart using an implantable medical device.

BACKGROUND OF THE INVENTION

A pacemaker is a medical device, typically implanted within a patient,which recognizes various dysrhythmias such as an abnormally slow heartrate (bradycardia) or an abnormally fast heart rate (tachycardia) anddelivers electrical pacing pulses to the heart in an effort to remedythe dysrhythmias. An ICD is a device, also implantable into a patient,which additionally recognizes atrial fibrillation (AF) or ventricularfibrillation (VF) and delivers electrical shocks to terminatefibrillation.

Pacemakers and ICD's carefully monitor characteristics of the heart suchas the heart rate to detect dysrhythmias, discriminate among differenttypes of dysrhythmias, identify appropriate therapy, and determine whento administer the therapy. The heart rate, for example, is monitored byexamining the electrical signals that are manifest concurrent with thedepolarization or contraction of the myocardial tissue of the heart. Theelectrical signals are detected internally by sensing leads mountedwithin the heart and are referred to as internal electrocardiogram(“IEGM”) signals. The normal contraction of atrial muscle tissue appearsas a P-wave within the IEGM. A sequence of consecutive P-waves definesthe atrial rate. The normal contraction of ventricular muscle tissueappears as an R-wave (sometimes referred to as the “QRS complex”) withinthe IEGM. A sequence of consecutive R-waves defines the ventricularrate. If the heart is subject to flutter or fibrillation, P-waves andR-waves typically cannot be discerned within the IEGM. Hence, thepacemaker or ICD may need to rely on other characteristics of the IEGMto discriminate among different types of flutter and fibrillation, toidentify optimal therapy, and to determine when to administer thetherapy. Some state of the art pacemakers and ICD□s are capable ofsensing electrical signals independently in the atria and in theventricles. Hence, an atrial IEGM and a separate ventricular IEGM aredetected. The atrial rate is determined based upon P-waves detected inthe atrial IEGM. The ventricular rate is determined based upon R-wavesdetected within the ventricular IEGM.

Thus pacemakers and ICD's administer therapy to the heart, in part,based upon the detection of electrical characteristics of the heart suchas P-waves, R-waves, atrial rate, ventricular rate, and the like. As onespecific example, if the atrial and ventricular rates are both below aminimum acceptable heart rate threshold or if long gaps appear withinthe IEGM signals wherein no P-waves and R-waves are sensed, the cardiacpacing device thereby concludes that the patient is suffering frombradycardia and administers pacing pulses in an effort to increase theheart rate or to eliminate long gaps without heart beats. As anotherspecific example, if the atrial and ventricular rates are well above amaximum expected heart rate, the cardiac pacing device concludes thatthe patient is suffering from a tachyarrhythmia and administersappropriate therapy such as, for example, overdrive pacing in an effortto lower the heart rate to within an acceptable range. If the atrialrate is found to be extremely high, but the ventricular rate isrelatively normal, the cardiac pacing device concludes that the patientis suffering from atrial flutter or atrial fibrillation and administersa defibrillation pulse to the atria. If the ventricular rate isextremely fast and chaotic, the cardiac pacing device concludes that thepatient is suffering from ventricular fibrillation and administers adefibrillation pulse directly to the ventricles. Details regardingtechniques for discriminating between atrial and ventriculardysrhythmias or arrhythmias are provided in U.S. Pat. No. 5,620,471 toDuncan entitled “System and Method for Discriminating Between Atrial andVentricular Arrhythmias and for Applying Cardiac Therapy Therefor”,issued Apr. 15, 1997, which is incorporated by reference herein.

Reliable operation of pacemakers and ICD□s therefore necessitates thatthe device be capable of accurately detecting P-waves, R-waves or otherelectrical events originating within the heart. Insofar as P-waves areconcerned, however, the aforementioned R-waves, though initiallygenerated within the ventricles, propagate into the atria and may bedetected therein as part of the atrial IEGM signal. It is thereforepossible for the device, upon detecting an electrical pulse within theatria, to misidentify a far-field R-wave as being a P-wave. As a result,any functions performed by the pacemaker which require accuratedetermination of P-waves may not function as intended. For example, PVCsmay be classified as P-R events so that the calculated atrial rate willbe higher than the actual atrial rate, perhaps causing the device toerroneously conclude that the atria are subject to a tachyarrhythmia,which does not in fact exist, or classify a ventricular tachycardia asan atrial tachycardia. Alternatively, the overestimated atrial heartrate may cause the device to fail to detect a bradycardia, which doesexist. As a result, inappropriate therapy may be administered. For anICD, an erroneously high determination of the atrial rate may cause theICD to incorrectly conclude that the heart is subject to atrialfibrillation, resulting in a potentially painful cardioversion pulseadministered to the atrium.

Thus, it is necessary to properly distinguish P-waves or otherelectrical events originating in the atria from far-field R-waves orother events originating in the ventricles. Accordingly, moststate-of-the-art pacemakers ignore any events detected within the atriaduring a predetermined period of time subsequent to the detection of anR-wave in the ventricles. This period of time is referred to as thepost-ventricular atrial blanking (PVAB) interval or a post-ventricularatrial refractory period (PVARP). Briefly, upon the detection of anR-wave from a sensing electrode positioned within the ventricles, thepacemaker thereafter ignores any events detected from a sensing leadwithin the atria for a period of time (e.g. 225 ms.) under theassumption that any event detected during that period of time isactually a far-field R-wave.

The use of the PVAB interval presupposes that the R-wave will bedetected in the ventricles before it appears as a far-field R-wave inthe atria. This is not always the case. The inventors of the presentinvention have determined that circumstances can arise wherein afar-field R-wave is detected within the atria before it is detectedwithin the ventricles. This may occur, for example, if an atrial sensinglead is positioned closer to the source of an R-wave than theventricular sensing leads. Another circumstance wherein an R-wave may bedetected within the atria without a preceding R-wave detection in theventricles occurs if the threshold for R-wave detection in theventricles is set too high, such that some R-waves are not detected atall within the ventricles. In any event, if the far-field R-wave isdetected within the atria without an immediately preceding R-wavedetection in the ventricles, the aforementioned PVAB interval isineffective to filter out the far-field R-wave from the atrial IEGM. Asa result, far-field R-waves are misclassified as P-waves resulting inincorrect determination of atrial rate, or other critical parameters,causing potentially erroneous therapy to be administered by thepacemaker. Although these problems have been described primarily withreference to the discrimination of P-waves from far-field R-waves,similar problems arise even in circumstances wherein P-waves and R-wavescannot be discerned within the IEGM, such as during flutter orfibrillation.

Accordingly, it would be highly desirable to provide an improvedtechnique for discriminating P-waves or other electrical eventsoriginating within the atria from far-field R-waves or other electricalevents originating within the ventricles, and it is to that end thataspects of the present invention are primarily directed.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, a method is provided fordiscriminating between electrical events originating in the atria fromelectrical events originating in the ventricles using an implantablemedical device employing a pre-ventricular blanking interval (pre-VAB).In accordance with the method, a determination is made as to whether anelectrical event detected within one of the ventricles was detectedwithin a predetermined pre-VAB interval following detection of anelectrical event within one of the atria. If so, the electrical event ofthe atria is rejected as being a far-field ventricular electrical eventor other non-atrial electrical event.

Within an exemplary embodiment, the electrical event of the atria is aP-wave and the electrical event of the ventricle is an R-wave. Theimplantable medical device determines whether the R-wave was detectedwithin a predetermined pre-VAB interval following detection of theP-wave and, if so, the P-wave is rejected as being a far-field R-wave.The implantable medical device is also configured to determine whetherthe P-wave was detected within a predetermined PVAB interval followingdetection of an R-wave in the ventricles and, if so, the P-wave islikewise rejected as being a far-field R-wave. In this manner, afar-field R-wave within the atria is properly rejected regardless ofwhether it is sensed before or after the R-wave of the ventricle.Accordingly, problems associated with misclassification of far-fieldR-waves are reduced or avoided completely. In other embodiments, theelectrical events within the atrial and ventricular IEGM signalsrepresent other detectable events besides P-waves or R-waves, such asevents detectable during flutter or fibrillation. Hence, the techniqueis not limited to processing atrial and ventricular IEGM signals inwhich P-waves and R-waves can be discerned but is applicable to othersituations as well.

In accordance with another aspect of the invention, a method is providedfor discriminating electrical events originating in the atria from otherelectrical events based upon template matching. In accordance with themethod, an electrical event detected within the atrium is comparedagainst a template representative of a true atrial event. If thedetected event substantially matches the template, the event is deemedto be a true atrial event; otherwise the event is discarded as being afar-field ventricular event or other anomalous electrical event. Withinan exemplary embodiment, the template is representative of the amplitudeshape of a P-wave, and hence the method discriminates true P-waves fromfar-field R-waves. In other embodiments, the template is representativeof other characteristics of a P-wave, such as its frequencycharacteristics, rather than its amplitude characteristics. In stillother embodiments, the template is representative of other electricallydetectable events, such as events occurring during flutter orfibrillation.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present invention may be morereadily understood by reference to the following description taken inconjunction with the accompanying drawings, in which:

FIG. 1 is a diagram of an ICD connected to the heart of a patient;

FIG. 2 is a flow chart illustrating a method employed by the ICD of FIG.1 to distinguish electrical events originating within the atria, such asP-waves, from electrical events not originating in the atria, such asfar-field R-waves using both pre-and post-ventricular atrial blankingintervals;

FIG. 3 is a graph illustrating atrial and ventricular IEGM signalsprocessed by the method of FIG. 2 and, in particular, illustrating trueand false P-waves;

FIG. 4 is a flow chart illustrating a method employed by the ICD of FIG.1 to distinguish electrical events originating within the atria, such asP-waves, from electrical events not originating in the ventricles, suchas far-field R-waves, using templates representative of true atrialevents;

FIG. 5 is a graph illustrating an atrial event and a templaterepresentative of a true P-wave processed by the method of FIG. 4; and

FIG. 6 is a functional block diagram of a dual-chamber implantablestimulation device that may be configured to perform the methods ofFIGS. 2-5.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the figures, preferred and exemplary embodiments ofthe invention will now be described. The embodiments will primarily bedescribed with reference to an ICD capable of detecting separate atrialand ventricular IEGM signals and configured for discriminating betweenevents appearing within the IEGM that originated within the atria andevents appearing within the IEGM that originated elsewhere. Hence, thefollowing description is not to be taken in a limiting sense but is mademerely for the purpose of describing the general principles of theinvention. The scope of the invention should be ascertained withreference to the issued claims. The following description includes thebest mode presently contemplated for practicing the invention. In thedescription of the invention that follows, like numerals or referencedesignators will be used to refer to like parts or elements throughout.

FIG. 1 illustrates a multi-chamber implantable stimulation device 10which is capable of treating both fast and slow arrhythmias withstimulation therapy, including cardioversion, defibrillation, and pacingstimulation. While a multi-chamber device is shown, this is forillustration purposes only, and one of skill in the art could readilyeliminate or disable the appropriate circuitry to provide asingle-chamber or dual-chamber stimulation device capable of treatingone or two chambers with cardioversion, defibrillation and pacingstimulation.

To provide right atrial chamber pacing stimulation and sensing, thestimulation device 10 is shown in electrical communication with apatient's heart 12 by way of an implantable atrial lead 16 having anatrial tip electrode 22 and (optionally) an atrial ring electrode (notshown) which typically is implanted in the patient's atrial appendage.

The stimulation device 10 is also shown in electrical communication withthe patient's heart 12 by way of an implantable ventricular lead 14having, in this embodiment, a ventricular tip electrode 24, aventricular ring electrode 25, a right ventricular (RV) coil electrode18, and an SVC coil electrode 20. Typically, the ventricular lead 14 istransvenously inserted into the heart 12 so as to place the RV coilelectrode 18 in the right ventricular apex, and the SVC coil electrode20 in the superior vena cava. Accordingly, the ventricular lead 14 iscapable of receiving cardiac signals, and delivering stimulation in theform of pacing and shock therapy to the right ventricle.

To sense left atrial and ventricular cardiac signals and to provide leftchamber pacing therapy, the stimulation device 10 is coupled to the“coronary sinus” lead 17 designed for placement in the “coronary sinusregion” via the coronary sinus os for positioning a distal electrodeadjacent to the left ventricle and/or additional electrode(s) adjacentto the left atrium. As used herein, the phrase “coronary sinus region”refers to the vasculature of the left ventricle, including any portionof the coronary sinus, great cardiac vein, left marginal vein, leftposterior ventricular vein, middle cardiac vein, and/or small cardiacvein or any other cardiac vein accessible by the coronary sinus. For acomplete description of a coronary sinus lead, see U.S. patentapplication Ser. No. 09/457,277, filed Dec. 8, 1999, entitled “ASelf-Anchoring, Steerable Coronary Sinus Lead” (Pianca et. al); and U.S.Pat. No. 5,466,254, “Coronary Sinus Lead with Atrial Sensing Capability”(Helland), which patents are hereby incorporated herein by reference.

As shown, the sensing/pacing locations are right atrium (high septalwall), left atrium (distal coronary sinus), right ventricular apex andleft ventricle (via a cardiac vein). In the exemplary embodiment, theICD combines signals received from the atrial sensing locations into asingle atrial IEGM signal and combines signals received from theventricular sensing locations into a single ventricular IEGM signal. Inother embodiments to be described below, the ICD processes the left andright IEGM signals separately.

Among other functions, the ICD analyzes the atrial and ventricular IEGMsignals to determine whether an atrial or ventricular tachyarrhythmia isoccurring and whether cardioversion/defibrillation therapy is required.Low energy therapy (e.g. antitachycardia pacing) may then be deliveredvia the sensing/pacing leads to the appropriate location(s). High energycardioversion/defibrillation pulses may be delivered to the atria viathe atrial shocking coils 19 and 20, or to the ventricles via theventricular shocking coil 18 with several shock vectors possible usingthe shocking coils and ICD case in various configurations. The ICDdetects numerous other types of dysrhythmias within the heart andprovides responsive therapy as well. Examples of other dysrhythmiasdetected by the ICD include bradycardia, supraventricular tachycardia(SVT) and the like.

Many of the functions performed by the ICD of FIG. 1 require accuratedetection of P-waves within the atrial IEGM signal. FIGS. 2 and 3illustrate a first technique for distinguishing P-waves (or otherelectrical events originating in the atria) from R-waves (or otherelectrical events not originating in the atria) so that functionsperformed by the ICD of FIG. 1 which rely on proper detection of atrialevents are operate more effectively.

Within FIG. 2, at step 100, the ICD receives and analyzes atrial IEGMsignals to detect electrical events represented therein. If the atriaare not currently subject to flutter or fibrillation, the detectedevents may be P-waves. If the atria are subject to flutter orfibrillation such that organized P-waves cannot easily be discerned, thedetected events may be voltage threshold crossings or other detectibleelectrical events. Herein, an electrically detectible event detectedwithin an atrial IEGM is referred to as an F_(A)-wave. Hence, a P-waveis one type of F_(A)-wave. At step 102, the ICD receives and analyzesventricular IEGM signals to detect electrical events, such as R-waves,represented therein. If the ventricles are not currently subject toflutter or fibrillation, the detected events may be R-waves. If theventricles are subject to flutter or fibrillation such that organizedR-waves cannot easily be discerned, the detected events may be voltagethreshold crossings or the like. Herein, an electrically detectibleevent detected within a ventricular IEGM signal is referred to as anF_(v)-wave. Hence, an R-wave is one type of F_(v)-wave. Steps 100 and102 are typically performed concurrently. At step 104, for each atrialevent that has been detected within the atrial IEGM signal, the ICDdetermines whether a corresponding ventricular event was detected withinthe ventricular IEGM signal within a pre-VAB period following detectionof the atrial event. In other words, upon detection of a P-wave, the ICDbegins tracking a pre-VAB period and determines whether an R-wave isdetected within the pre-VAB period.

The pre-VAB interval is illustrated within FIG. 3. Briefly, FIG. 3illustrates an atrial IEGM signal 106 and a ventricular IEGM signal 108.The atrial IEGM signal includes various events detected therein.Beginning at each event detected within the atrial IEGM, the ICD tracksa pre-VAB period 110 and determines whether a ventricular event isdetected within the ventricular IEGM within that time period. If aventricular event is detected within the pre-VAB time period, then theatrial event is discarded as being a far-field ventricular event. WithinFIG. 3, one of the ventricular events (112) is detected within thepre-VAB period of a preceding atrial event (113). Accordingly, atrialevent 113 is discarded as being a far-field ventricular event. Note thatthe far-field ventricular event is actually detected within the atrialIEGM signal before the event is detected within the ventricular IEGMsignal. As discussed above, this may occur if the atrial sensing lead iscloser to the portion of the ventricle wherein the R-wave originatesthan the ventricular sensing lead. The duration of the pre-VAB period ispreferably a programmable feature of the ICD. In one example, thepre-VAB period is programmable within the range of 0-60 milliseconds.

Referring again to FIG. 2, if a ventricular event is detected within thepre-VAB period, step 114, then the atrial event is discarded as being afar-field ventricular event, step 116. Then, for each ventricular event,the ICD determines at step 118 whether an atrial event is detectedwithin a post-VAB period following detection of the ventricular event.This is also illustrated within FIG. 3 wherein a post-VAB period 120begins upon detection of each ventricular event detected within theventricular IEGM signal. One of the atrial events (124) is detectedwithin the post-VAB period of a preceding ventricular event (125).Accordingly, atrial event 124 is discarded as being a far-fieldventricular event. Thus, referring again to FIG. 2, if the atrial eventis detected within the post-VAB period at step 126, then the atrialevent is rejected at step 128 as being a far-field ventricular event.The duration of the post-VAB period is also preferably a programmableparameter of the ICD. In one example, the post-VAB period isprogrammable within the range of 10-250 milliseconds.

At step 130, the ICD analyzes all ventricular events and any remainingatrial events to detect dysrhythmias, if any, occurring within the heartand to administer appropriate therapy. As noted above, the dysrhythmiasmay be, for example, bradycardia, tachycardia, atrial flutter, or otherdysrhythmias. The appropriate therapy administered by the ICD dependsupon the nature of the dysrhythmia and may include, for example,anti-bradycardial pacing, anti-tachycardial pacing, or theadministration of atrial or ventricular cardioversion pulses. Someexemplary techniques for administering therapy are provided in theabove-referenced U.S. Pat. No. 5,620,471 to Duncan. Note, also, thatwithin step 130 all other functions performed by the ICD which requirereliable detection of atrial events are thereby rendered more accurateby properly eliminating all far-field R-waves, or other far-fieldventricular events, from the atrial IEGM signal. Thus, for example, ICDfunctions involving upper rate limit bradycardial functions such as 2:1block response mode or Wenkebach mode operate more effectively. Detailsregarding 2:1 block response mode is provided within U.S. Pat. No.5,601,613 to Florio et al., entitled “Method and Apparatus for ProvidingEnhanced 2:1 Block Response with Rate-Responsive AV Delay in aPacemaker”, issued Feb. 11, 1997, which is incorporated by referenceherein. Details regarding Wenkebach mode are provided in U.S. Pat. No.5,788,717 to Mann et aL, entitled “Atrial Rate Determination and AtrialTachycardia Detection in a Dual-Chamber Implantable Pacemaker”, issuedAug. 4, 1998, which is incorporated by reference herein. Other functionswhich benefit from proper discrimination of true atrial events fromother events detected within the atrial IEGM signal include modeswitching functions and the like. Details regarding mode switchingfunctions are provided in U.S. Pat. No. 5,342,405 to Duncan, entitled“System and Method for Selecting a Mode of Operation of a Dual-ChamberPacemaker”, issued Aug. 30, 1994, which is also incorporated byreference herein. Also, within step 130 the ICD may record the detectionof each electrical event in the atrial IEGM signal along with anindication of whether the event was rejected as being a far-field eventof the ventricle. The ICD may further record an indication of whetherthe rejected event was rejected as being within the pre-VAB period orwithin the post-VAB period.

With reference to FIGS. 4 and 5, a second technique for discriminatingtrue atrial events from other events will now be described. Beginning atstep 200 of FIG. 4, the ICD receives and analyzes atrial IEGM signals todetect electrical events therein. If the atria are not subject tofibrillation of flutter, the atrial events may be P-waves. Otherwise,the atrial events may be other types of F_(A)-waves. In somecircumstances, even if the atria are not subject to flutter orfibrillation, it may be appropriate to detect other types of F_(A)-wavesbesides P-waves. In any case, at step 202 the ICD receives and analyzesventricular IEGM signals to detect electrical events, such as R-waves,therein. Then, for each atrial event, the ICD compares the atrial eventat step 204 with a predetermined template representative of true atrialevents to determine whether the detected atrial event matches thetemplate. This is illustrated in FIG. 5.

Briefly, FIG. 5 provides an atrial IEGM signal 206 in which numerousdetected events are illustrated. FIG. 5 also illustrates a template 208representative of a true P-wave. Within step 204 of FIG. 4, the ICDcompares each event detected within the atrial IEGM with the template todetermine if there is a substantial similarity. Atrial events such asevents 210 and 212 substantially match the P-wave template and therebyare deemed to be true P-waves. However, events 214 and 216 do notsubstantially match the P-wave template and therefore are discarded asnot being true P-waves. Indeed, as can be seen within FIG. 5, events 214and 216 are actually far-field R-waves. Referring again to FIG. 4, ifthe atrial events do not match the template at step 218, the atrialevent is rejected at step 220 as being a far-field ventricular event orother non-atrial event. Otherwise, the atrial event is not rejected. Ineither case, at step 222 the ICD analyzes the ventricular events and anyremaining atrial events to detect dysrhythmias, if any, in the heart andto administer appropriate therapy or to perform any other functionrequiring accurate identification of atrial events.

The P-waves and far-field R-waves illustrated in FIG. 5 are representedas stylized events for clarity in illustrating the concept of theinvention. In practical applications, the atrial IEGM signal is subjectto considerable noise. Accordingly, in some implementations, the atrialIEGM signal may be filtered prior to comparison against the template tohelp prevent noise from interfering with the comparison. Also, thecomparison between the detected events and the template need not requirean absolute match. Rather, it is sufficient that the detected atrialevent correspond to the template to within some predetermined thresholdof variation. The exact threshold depends upon the particularcharacteristics represented by the template and upon the amount of noisein the atrial IEGM signal. The appropriate threshold, in eachimplementation, may be determined for example by performing routineexperimentation using test atrial IEGM signals against stored testtemplates.

Further with regard to FIG. 5, although the example illustrated thereinprovides a P-wave template representative of the shape of a true P-wave,alternative templates may be employed which represent other detectablecharacteristics of true atrial events. For example, the template mayrepresent only the frequency content of true atrial events. If so, theevents detected within the atrial IEGM signal are processed to extractthe frequency components therein using, for example, a conventionalfrequency extraction method such as the Fast Fourier Transform (FFT).The frequency components extracted from the atrial IEGM signal are thencompared with the frequency components stored in the template. If thefrequency components of the atrial IEGM signal substantially match thoseof the template, a conclusion is drawn that the atrial event is a trueatrial event. Numerous other features representative of true atrialevents may be alternatively represented within a template for comparisonagainst corresponding features of the atrial IEGM signal. In someimplementations, two or more templates representative of differentfeatures are employed to provide more reliable rejection of non-atrialevents. For example, one template represents the amplitude components ofa true atrial event, whereas another template represents the frequencycomponents of a true atrial event.

Also, the specific template used may depend upon the current status ofthe ICD and upon the current dysrhythmia, if any, detected within theheart. For example, if the ICD has already determined that the heart issubject to flutter, then a template representative of an atrial waveform expected to occur during flutter may be employed. On the otherhand, if the ICD has determined that the atria are subject to atachycardia, then a wave form representative of a tachycardial P-wavemay be employed. The shape of the template also may be modulated basedupon the current detected atrial rate. As can be appreciated, numerousmodifications may be provided to the examples described herein inaccordance with the general concept of the invention.

Finally with respect to both FIGS. 3 and 5, the IEGM signals illustratedtherein show P-waves and R-waves. Alternatively, other electrical eventsmay be detected. Examples include some predetermined number ofconsecutive zero voltage crossings or the like.

Although described with respect to examples wherein atrial signals fromthe left and right atria are merged to yield a single atrial IEGM signaland wherein ventricular signal from the left and right atria are mergedto yield a single ventricular IEGM signal, the invention is alsoapplicable to discriminating atrial events from non-atrial events usingthe separate left and right atrial and ventricular IEGM signals. In oneexample, the left atrial IEGM is compared with only the left ventricularIEGM using the pre-VAB. Likewise, the right atrial IEGM is compared withonly the right ventricular IEGM using the pre-VAB. A P-wave is rejectedif either the left or right IEGM comparison identifies the P-wave asbeing a far-field R-wave. In other implementations, the P-wave isrejected only if both the left and right IEGM comparisons identify theP-wave as being a far-field R-wave. In implementations wherein templatematching is employed and multiple atrial IEGM signals are processed, aP-wave is rejected as being a far-field R-wave if the P-wave within anyone of the atrial IEGM signals fails to match the template. In otherimplementations, the P-wave is rejected only if all of therepresentations of the P-wave within all of the atrial IEGM signals failto match the template. As can be appreciated, numerous variations areconsistent with the general scope of the invention. Aspects of theinvention as it pertains to the discrimination of atrial events fromventricular events are also applicable to techniques for determiningperiods of electrical coherence within the heart for the purposes, forexample, of administering cardioversion pulses during periods ofcoherence. These techniques are described in greater detail in copendingU.S. Provisional Patent Application Ser. No. 60/173,341, filed Dec. 28,1999, entitled “Method and Apparatus for Detecting Natural ElectricalCoherence Within the Heart and for Administering Therapy Based Thereon”,assigned to the assignee of the present invention, and incorporated byreference herein.

FIG. 6 illustrates internal components of an ICD that configured toperform the method described above in connection with FIGS. 2-5.

The housing 340 for the stimulation device 10, shown schematically inFIG. 6, is often referred to as the “can”, “case” or “case electrode”and may be programmably selected to act as the return electrode for all“unipolar” modes. The housing 340 may further be used as a returnelectrode alone or in combination with one or more of the coilelectrodes, 18, 19 or 20, for shocking purposes. The housing 340 furtherincludes a connector (not shown) having a plurality of terminals, 342,344, 346, 348, 352, 354, 356, and 358 (shown schematically and, forconvenience, the names of the electrodes to which they are connected areshown next to the terminals). As such, to achieve right atrial sensingand pacing, the connector includes at least a right atrial tip terminal(A_(R) TIP) 342 adapted for connection to the atrial tip electrode 22.

To achieve left chamber sensing, pacing and shocking, the connectorincludes at least a left ventricular tip terminal (V_(L) TIP) 344, aleft atrial ring terminal (A_(L) RING) 46, and a left atrial shockingterminal (A_(L) COIL) 348, which are adapted for connection to the leftventricular ring electrode 25, the left atrial electrode 26, and theleft atrial coil electrode 19, respectively.

To support right chamber sensing, pacing and shocking, the connectorfurther includes a right ventricular tip terminal (VR_(R) TIP) 352, aright ventricular ring terminal (V_(R) RING) 354, a right ventricularshocking terminal (RV COIL) 356, and an SVC shocking terminal (SVC COIL)358, which are adapted for connection to the right ventricular tipelectrode 24, right ventricular ring electrode 25, the RV coil electrode18, and the SVC coil electrode 20, respectively.

At the core of the stimulation device 10 is a programmablemicrocontroller 360 which controls the various modes of stimulationtherapy and performs, in combination with other units of the ICD, themethods described above in connection with FIGS. 2-5. As is well knownin the art, the microcontroller 360 includes a microprocessor, orequivalent control circuitry, designed specifically for controlling thedelivery of stimulation therapy and may further include RAM or ROMmemory, logic and timing circuitry, state machine circuitry, and I/Ocircuitry. Typically, the microcontroller 360 includes the ability toprocess or monitor input signals (data) as controlled by a program codestored in a designated block of memory. The details of the design andoperation of the microcontroller 360 are not critical to the presentinvention. Rather, any suitable microcontroller 360 may be used thatcarries out the functions described herein. The use ofmicroprocessor-based control circuits for performing timing and dataanalysis functions is well known in the art. As shown in FIG. 6, anatrial pulse generator 370 and a ventricular pulse generator 372generate pacing stimulation pulses for delivery by the atrial lead 16and the ventricular lead 14, respectively, via a switch bank 374. Thepulse generators, 370 and 372, are controlled by the microcontroller 360via appropriate control signals, 376 and 378, respectively, to triggeror inhibit the stimulation pulses. The microcontroller 360 furtherincludes timing circuitry that controls the operation of the stimulationdevice timing of such stimulation pulses that is well known in the art.

The switch bank 374 includes a plurality of switches for switchablyconnecting the desired electrodes to the appropriate I/O circuits,thereby providing complete electrode programmability. Accordingly, theswitch bank 374, in response to a control signal 380 from themicrocontroller 360, determines the polarity of the stimulation pulses(e.g., unipolar or bipolar) by selectively closing the appropriatecombination of switches (not shown) as is known in the art.

An atrial sense amplifier 382 and a ventricular sense amplifier 384 arealso coupled to the atrial and ventricular leads, 16 and 14,respectively, through the switch bank 374 for detecting the presence ofcardiac activity. The switch bank 374 determines the “sensing polarity”of the cardiac signal by selectively closing the appropriate switches,as is also known in the art. In this way, the clinician may program thesensing polarity independent of the stimulation polarity.

Each sense amplifier, 382 and 384, preferably employs a low power,precision amplifier with programmable gain and/or automatic gaincontrol, bandpass filtering, and a threshold detection circuit, known inthe art, to selectively sense the cardiac signal of interest. Theautomatic gain control enables the device 10 to deal effectively withthe difficult problem of sensing the low frequency, low amplitude signalcharacteristics of ventricular fibrillation. The outputs of the atrialand ventricular sense amplifiers 382 and 384 are connected to themicrocontroller 360, which, in turn, inhibit the atrial and ventricularpulse generators 370 and 372, respectively, in a demand fashion whenevercardiac activity is sensed in the respective chambers.

For arrhythmia detection is typically performed by the microcontroller360, in conjunction with the atrial and ventricular sense amplifiers 382and 384 to sense cardiac signals to determine whether a rhythm isphysiologic or pathologic. As used herein “sensing” is reserved for thenoting of an electrical depolarization, and “detection” is theprocessing of these sensed depolarization signals and noting thepresence of an arrhythmia. The timing intervals between sensed events(e.g., the P—P and R—R intervals) are then classified by themicrocontroller 360 by comparing them to a predefined rate zone limit(i.e., bradycardia, normal, low rate VT, high rate VT, and fibrillationrate zones) and various other characteristics (e.g., sudden onset,stability, physiologic sensors, and morphology, etc.) in order todetermine the type of remedial therapy that is needed (e.g., bradycardiapacing, anti-tachycardia pacing, cardioversion shocks or defibrillationshocks, also known as “tiered therapy”).

Cardiac signals are also applied to the inputs of an analog to digital(A/D) data acquisition system 390. The data acquisition system 390 isconfigured to acquire intracardiac electrogram signals, convert the rawanalog data into a digital signal, and store the digital signals forlater processing and/or telemetric transmission to an external device402. The data acquisition system 390 is coupled to the atrial andventricular leads, 16 and 14, through the switch bank 374 to samplecardiac signals across any pair of desired electrodes.

The microcontroller 360 is further coupled to a memory 394 by a suitabledata/address bus 396, wherein the programmable operating parameters usedby the microcontroller 360 are stored and modified, as required, inorder to customize the operation of the stimulation device 10 to suitthe needs of a particular patient. Such operating parameters define, forexample, pacing pulse amplitude, pulse duration, electrode polarity,rate, sensitivity, automatic features, arrhythmia detection criteria,and the amplitude, waveshape and vector of each shocking pulse to bedelivered to the patient's heart 328 within each respective tier oftherapy.

Advantageously, the operating parameters of the implantable device 10may be non-invasively programmed into the memory 394 through a telemetrycircuit 400 in telemetric communication with an external device 402,such as a programmer, transtelephonic transceiver, or a diagnosticsystem analyzer. The telemetry circuit 400 is activated by themicrocontroller by a control signal 406. The telemetry circuit 400advantageously allows intracardiac electrograms and status informationrelating to the operation of the device 10 (as contained in themicrocontroller 360 or memory 394) to be sent to the external device 402through the established communication link 404. In the preferredembodiment, the stimulation device 10 further includes a physiologicsensor 410. Such sensors are commonly called “rate-responsive” sensors.The physiological sensor 410 is used to detect the exercise state of thepatient, to which the microcontroller 360 responds by adjusting the rateand AV Delay at which the atrial and ventricular pulse generators 370and 372 generate stimulation pulses. The type of sensor used is notcritical to the present invention and is shown only for completeness.

The stimulation device additionally includes a battery 414, whichprovides operating power to all of the circuits shown in FIG. 6. For thestimulation device 10, which employs shocking therapy, the battery mustbe capable of operating at low current drains for long periods of time,and then be capable of providing high-current pulses (for capacitorcharging) when the patient requires a shock pulse. The battery 414 mustalso have a predictable discharge characteristic so that electivereplacement time can be detected. Accordingly, the present inventionemploys lithium/silver vanadium oxide batteries, as is true for most (ifnot all) such devices to date.

As further shown in FIG. 6, the ICD of the invention may include animpedance measuring circuit 420 which is enabled by the microcontroller360 by a control signal 422. The impedance measuring circuit 420 is notcritical to the present invention and is shown for only completeness.

The ICD detects the occurrence of an arrhythmia, and automaticallyapplies an appropriate electrical shock therapy to the heart aimed atterminating the detected arrhythmia. To this end, the microcontroller360 further controls a shocking circuit 430 by way of a control signal432. The shocking circuit 430 generates shocking pulses of low (up to0.5 joules), moderate (0.5-10 joules), or high energy (11 to 40 joules),as controlled by the microcontroller 360. Such shocking pulses areapplied to the patient's heart through at least two shocking electrodes,and as shown in this embodiment, using the RV and SVC coil electrodes 18and 20, respectively. In alternative embodiments, the housing 340 mayact as an active electrode in combination with the RV electrode 18alone, or as part of a split electrical vector using the SVC coilelectrode 20 (i.e., using the RV electrode as common).

Cardioversion shocks are generally considered to be of low to moderateenergy level (so as to minimize pain felt by the patient), and/orsynchronized with an R-wave and/or pertaining to the treatment oftachycardia. Defibrillation shocks are generally of moderate to highenergy level (i.e., corresponding to thresholds in the range of 5-40joules), delivered asynchronously (since R-waves may be toodisorganized), and pertaining exclusively to the treatment offibrillation. Accordingly, the microcontroller 360 is capable ofcontrolling the synchronous or asynchronous delivery of the shockingpulses.

Aspects of the invention may be embodied within software running withina programmable processor within the device or may be implemented ashard-wired logic within an application specific integrated circuit(ASIC) or the like.

Accordingly, and as one of skill in the art can appreciate, the presentinvention can be employed with the microcontroller system described inFIG. 6. What has been described are various techniques fordiscriminating true atrial events from non-atrial events and foradjusting or administering therapy based thereon. Aspects of theinvention are also applicable to discriminating true ventricular eventssuch as R-waves from non-ventricular events such as P-waves. In general,the embodiments described herein are merely illustrative of theinvention and should not be construed as limiting the scope of theinvention, which is to be interpreted in accordance with the claims thatfollow.

What is claimed is:
 1. A method for discriminating electrical eventsoriginating in the atria from electrical events originating with theventricles of a heart using an implantable medical device receivingsignals detected from within an atrium of the heart and receivingsignals detected from within a ventricle of the heart, the methodcomprising the steps of: detecting an electrical event within theatrium; detecting an electrical event within the ventricle; anddetermining whether the electrical event occurring within the ventriclewas detected within a predetermined pre-ventricular blanking intervalfollowing detection of the electrical event occurring within the atriumand, if so, rejecting the electrical event of the atrium as being afar-field electrical event of the ventricle.
 2. The method of claim 1,further comprising the step of: determining whether the electrical eventof the atrium was detected within a predetermined post-ventricularblanking interval following detection of the electrical event of theventricle and, if so, rejecting the electrical event of the atrium asbeing a far-field electrical event of the ventricle.
 3. The method ofclaim 1, wherein the electrical event of the atrium is a P-wave.
 4. Themethod of claim 1, wherein the electrical event of the ventricle is anR-wave.
 5. The method of claim 1, further comprising the step of:administering therapy based upon the detected events of the ventriclesin combination with the detected events of the atrium not rejected asbeing far-field events of the ventricle.
 6. The method of claim 5,wherein the step of administering therapy includes the steps of:identifying an dysrhythmia, if any, in the heart; determining therapy tobe applied to remedy the dysrhythmia; and applying the therapy to theheart.
 7. The method of claim 6, wherein the dysrhythmia is bradycardia,tachycardia, fibrillation or flutter.
 8. The method of claim 1, furthercomprising the step of performing functions based, in part, on thedetected events of the atrium not rejected as being far-field events ofthe ventricle.
 9. The method of claim 8, wherein the step of performingfunctions includes the steps of performing mode switching functions,pre-ventricular contraction detection functions, PV tracking functions,2:1 blocking functions, and Wenkebach mode functions.
 10. A system fordiscriminating electrical events originating in the atria fromelectrical events originating with the ventricles of a heart using animplantable medical device receiving signals detected from within anatrium of the heart and receiving signals detected from within aventricle of the heart, the system comprising: means for detecting anelectrical event occurring within the atrium; means for detecting anelectrical event occurring within the ventricle; and means fordetermining whether the electrical event occurring within the ventriclewas detected within a predetermined pre-ventricular blanking intervalfollowing detection of the electrical event occurring within the atriumand, if so, for rejecting the electrical event occurring within theatrium as being a far-field electrical event of the ventricle.
 11. Thesystem of claim 10, further comprising: means for determining whetherthe electrical event of the atrium was detected within a predeterminedpost-ventricular blanking interval following detection of the electricalevent of the ventricle; and means, responsive to a determination thatthe electrical event of the atrium was detected within the predeterminedpost-ventricular blanking interval, for rejecting the electrical eventof the atrium as being a far-field electrical event of the ventricle.12. The system of claim 10, further comprising means for administeringtherapy based upon the detected events of the ventricles in combinationwith the detected events of the atrium not rejected as being far-fieldevents of the ventricle.
 13. A system for discriminating electricalevents originating in the atria from electrical events originating withthe ventricles of a heart using an implantable medical device receivingsignals detected from within an atrium of the heart and receivingsignals detected from within a ventricle of the heart, the systemcomprising: an atrial sense amplifier for detecting an electrical eventoccurring within the atrium; an ventricular sense amplifier fordetecting an electrical event occurring within the ventricle; and acontroller for determining whether the electrical event occurring withthe ventricle was detected within a predetermined pre-ventricularblanking interval following detection of the electrical event occurringwithin the atrium and, if so, rejecting the electrical event of theatrium as being a far-field electrical event of the ventricle.
 14. Thesystem of claim 13, wherein the controller also determines whether theelectrical event of the atrium was detected within a predeterminedpost-ventricular blanking interval following detection of the electricalevent of the ventricle and, if so, rejects the electrical event of theatrium as being a far-field electrical event of the ventricle.
 15. Thesystem of claim 13, wherein the controller also generates therapy forapplying to the heart based upon the detected events of the ventriclesin combination with the detected events of the atrium not rejected asbeing far-field events of the ventricle.